Steps to reproduce:
1. Open the attached project 'case_790378-SpriteSlice'
2. Open 'SmallObjectsSheet' with Sprite Editor
3. Notice that switching between sprites temporarily freezes the Editor when selecting 'SmallObjectsSheet'
4. In the Sprite Editor click 'Slice/Slice' to slice the sprite sheet automatically
5. Notice that switching between sprites no longer freezes when selecting 'SmallObjectsSheet'

Expected: Freeze should not occur

Reproduced with: 5.3.2p1, 5.3.3p3, 5.3.4p4, 5.4.0b15 (Regression from from 5.3.1p4 to 5.3.2p1)
Not reproducable: 5.1.3p3, 5.2.3p3, 5.3.1p4, 5.3.2f1